Oxidation process employing sulfites or bisulfites



3,022,341 OXIDATION PROCESS EMPLOYING SULFITES OR BISULFITES William G. Toland, Jr., San Rafael, Calif assiguor to California Research Corporation, San Francisco, Calif.,

a corporation of Delaware No Drawing. Filed Sept. 25, 1958, Ser. No. 763,190

6 Claims. (Cl. 260-524) This application is a continuation-impart of my copending application Serial No. 374,426, now abandoned,

States ate filed August 14, 1953 as a continuation-impart of my are too severe, considerable losses of the charging stock are sustained by r ason of ring ruptures of the aromatic nuclei. If the onditions under which the oxidation is conducted are not sufliciently severe, large proportions of the charging stockare converted to oxidation products which are intermediate between the charging stock and the desired carboxylic acids.-

It is an object of this invention to provide a method by which alkyl aromatic hydrocarbons may be converted to aromatic carboxylic acids having the carboxyl group or groups directly attached to the nuclear carbon atom or atoms at high yields. I

It has now been found that lower alkyl aromatic hydrocarbons, lower alkyl benzoic acids, and partial oxidation products of such hydrocarbons and acids,- for example, alcohols, aldehydes, kctones, and the like, may be oxidized to produce aromatic carboxylic acids by heating a mixture consisting essentially of any of these materials, water, and ammonium sul-fite orammonium bisulfite to a temperature in the range from 500 to 700 F. under a superatmospheric pressure sufficient to maintain a part of the Water-in liquid phase. Preferably, about 1 mol of sulfite or bisulfi-te per mol of methyl group to be oxidized should, be used-in the process of the present invention; however, those'skilled in the art will recognize that other quantities will be operable. Generally, about 0.5-5.0 mols of sulfite or bisulfite per rncl of methyl group to be oxidized will be satisfactory.

The nature of the reaction occurring in the process of this invention is illustrated by the following equation:

COONHa U E (NHO present in the reaction mixture as an amide which requires a hydrolysis step to liberate the acid.

US. Patent No. 2,610,980 shows the employment of the Willgerodt reaction to oxidize alkyl aromatic hydrocarbons such as xylenes. In this reaction sulfur is the oxidizing agent and 3 atoms of sulfur are required to oxidize one methyl group to a carboxyl group, the carboxyl group being converted in the course of the reaction to the amide. In the process of the present invention a small amount of elemental sulfur not usually exceeding about 6% of the amount which would be required if elemental sulfur were to be provided as the sole oxidizing agent may be introduced into the reaction mixture. 2% to 10% of the amount of sulfur which would suffice to oxidize the feed if sulfur alone were the oxidizing agent may be employed. This small amount of sulfur acts as an initiator and shortens the total time required for completion of the reaction. A small amount of a Water-soluble sulfide may also be used as an initiator. The addition of from 0.05 to 0.3 mol of either a water-so-lnble sulfide or elemental sulfur per mol of methyl group to be oxidized to the reaction mixture insures rapid attainment of a high oxidation rate. I

The reaction should be conducted at temperatures above about 500 F. At lower temperatures the rate of reaction is low. The maximum temperature of reaction should be below the critical temperature of water in order that a liquid aqueous phase may be present in the reaction mixture. Preferably, the reaction is conducted at temperatures in the range from about 550 to 675 F., from 600 to 650 F. being optimum.

The pressure is a "dependent variable in the reaction and is usually in the range from about 1000 to 5000 p.s.i.g., which insures the presence of a liquid aqueous phase. The pressure may be controlledduring the reaction by bleeding off a portion of the gas formed during the reaction. I"

The invention Will be'understood upon consideration of the following examples which are provided to illustrate the character of the reactions which produce the desired aromatic carboxylic acids and their derivatives, but which are not intended, in and of themselves, to mark out the limits of the invention.

, EXAMPLE 1 7.1 g. of a technical grade of a-methylnaphthalene, 20

cc. of ammonium polysulfide-ammonium bisulfitesolution, and 20 cc. of water were charged to a 250 cc. shaking autoclave. The ammonium polysulfide-ammonium bisulfite solution, with the ammonium polysulfide component being present as an initiator for the primaryoxidation reaction, was prepared bysuspending sulfur'in ammonium hydroxide, bubbling in hydrogen sulfide, and then bubbling in sulfur dioxide; ijts oxidizing power was such that 6 cc. of the solution were stoichiometricallysufficient to oxidize 1 cc. of xylene to phthalic acid. The autoclave was sealed, heated to a temperature ranging from 550 to 590 F., and shaken for one hour. The autoclave was cooled, depressured, and opened. The reaction product consisted of a light brown slurry and some black tarry residue. 10 g. of sodium hydroxide were added to the reaction product mixture andit'was then steam stripped to remove ammonia. 200 cc. of distillate were collected during the steam stripping which were found to contain 0.3 g. of unreacted a-methylnaphthalene. The stripped reaction product was filtered hot to remove tar, chilled, and filtered again. The second filtration yielded 7 0.4 g. of neutral light yellow crystalline material of undetermined composition. The filtrate from the second filtration was acidified to a pH 6 and filtered hot to remove frec sulfur. Charcoal was added to the last-mention filtrate and it was refiltered, the filtrate acidified to pH.v Zto precipitate acids, and the acidifiedfiltrate was filtered to separate a filter-.cake comprising the acidic material. This latter filter cake was washed and dried.

neutral equivalent was 172. 'EXAMPLE 2 {1 mold a mixture of metaand paraxylene containing 85% metaxylene, 1.55 mols of hydrogen sulfide, 58 mols of water, and -1.5;mol s of ammonium sulfite in the form of 1.53 mols of sulfur dioxide plus 3.08 mols of ammonia were charged to a bomb reactor which was sealed and heated to 600 F. for 60 minutes. The pressure attained a maximum of 2575 p.s.i.g. The bomb was cooled to 70 F. and deprcssured. The liquid product was slurried with a small amount of activated charcoal and filtered to remove color bodies. After acidification, it was found that 96.5% of the xylene feed was converted to an acidamide mixture product having a saponification equivalent of 86 and a neutral equivalent of 101.5. After saponification, a 91.7 mol percent of mixed isoand terephthalic acid based on the xylene converted was recovered.

EXAMPLE 3 A 2.5 liter autoclave was charged with 0.71 mol of an 85-15 ratio of metaxylene-paraxylene, 1.54 mols of ammonium sulfite, 1.55 mols of ammonium bisulfide, and 32 mols of water. The mixture was heated to 600 F. with shaking for one hour and attained a maximum pressure of 2550 p.s.i.g. Workup of the products showed the presence of 0.025 mol of unreacted xylene, 0.029 mol of toluic acids, and 0.596 mol of phthalic acids. This represents a 96.7% conversion with an 87.2% yield of phthalic acids and a 4.2% yield of toluic acid.

EXAMPLE 4 A 2.5 liter autoclave was charged with 0.707 mol of 85l5 metaxylene-paraxylene, 1.39 mols of ammonium bisulfite, 1.67 mols of ammonium bisulfide, and 21 mols of water. The mixture was heated to 600 F. for. 40 minutes and reached a maximum pressure of 2300 pounds. The products were shown to contain 0.028 mol of unreacted xylene, 0.04 mol of toluic acids, and 0.518 mol of phthalic acids. This represents a 96.1% conversion with a 76.4% yield of phthalic acids and 5.9% yield of toluic acids.

The following Table I indicates the nature of the oxidation reaction with a variety of organic compounds at temperatures in the range 500 to 700 F. employing the oxidizing agent of the present invention:

Table I Material Reaction Product Phthalic acids. Carbon dioxide.

Do. Acetic acid, succinic acid, butyric acid, 002.

Acetophenone-.--. Benzoic acid.

Do Phenylacetic acid. Cyclohexanone. Phenol and C02. a-Methyl naphthale a-Naphthoic acid.

p-Tertiary-butyl toluene.

p-Tertiary-butyl benzoic acid. Toluene Benzoic acid.

Mesitylene Trimesic acid.

Pscudocumene Orthophthalic, isophthalic, and

' terephthalic acids.

lsophthalic acid.

Benzoic acid. Iso-terephthalic acids. 00:, iso-butyric acid. CO1, lower aliphatic acids.

n-Hexane Table I?Continued Material Reaction Product n-Octane %owertahliphatific acids (NE -154) rime y ace 10 act m pentane {grimeggyl progioniedacid. rlme y ace 0 am 5 ti y hexane {Trimethyl propionic acid. Diamyl sulfide Mixed acids, predominantly valeric 1 g acid (NE -110). t-Butyl p-xylene t tl-gutytlhtelrephghalicgcid. lme y ace 1cac1 Di isobutylene {Trimethyl propionic acid. Eemimellitene Phthalic acids. I=Iethanol CO2. Trimethylamine. Methyl mercaptan, CO1. Dodeccne (propylene polymer) Aliphatic acids (NE 284.8). t-Butyl meta-xylene. t-Butyl isophthalic acid. Sucrose Acetic acid,CO2. n-Butane. Do. Benzene. CO, 00:. Methane. C0, C01. Benzylami Benzoic acid.

The process of the present invention requires only one atomic equivalent of sulfur in the form of SO to oxidize one atomic equivalent of carbon in the form of a methyl group to its corresponding carboxyl group, and only one mol of H 3 is produced per carboxyl group. In contrast, a conventional sulfur oxidation process employing sulfur and ammonia a the'oxidizing agent requires the use of three atomic equivalents of sulfur to achieve the desired result, and three mols of H 8 per carboxyl group are produced, thereby necessitating larger reactor volume per unit of product, a more extensive H S recovery system. Further, the increased H S partial pressure in the sulfur-ammonia system reduces the oxidation potential and increases the difiiculty in driving the reaction to completion. When employing ammonium sulfite or ammonium bisulfite in accordance with the present invention, there is materially less amide product formed than in a sulfur.

ammonia system.

What is claimed is:

, 1. A process for oxidizing a material of the group consisting of methyl-substituted aromatic hydrocarbons and aromatic carboxylic acids having at least one nuclear hydrogen replaced by a methyl group which comprises heating a mixture consisting essentially of said material, water and an agent selected from the class consisting of ammonium sulfite and ammonium bisulfite to a temperature in the range from 500 to 700 F. under a superatmospheric pressure sutficient to maintain a part of the water in liquid phase.

2. A process as in claim 1, wherein said agent is an ammonium sulfite.

3. A process as in claim 1, wherein said agent is an ammonium bisulfite.

4. A process as in claim 1, wherein said material is a xylene and said agent is ammonium sulfite.

5. A process as in claim 1, wherein said material is a xylene and said agent is ammonium bisulfite.

6. A process as in claim 1, with the addition of about 0.05 to 0.3 mol of a sulfur compound selected from the group consisting of water-soluble sulfides and elemental sulfur per mol of methyl group contained in the material to be oxidized to accelerate the oxidation reaction.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR OXIDIZING A MATERIAL OF THE GROUP CONSISTING OF METHYL-SUBSTITUTED AROMATIC HYDROCARBONS AND AROMATIC CARBOXYLIC ACIDS HAVING AT LEAST ONE NUCLEAR HYDROGEN REPLACED BY A METHYL GROUP WHICH COMPRISES HEATING A MIXTURE CONSISTING ESSENTIALLY OF SAID MATERIAL, WATER AND AN AGENT SELECTED FROM THE CLASS CONSISTING OF AMMONIUM SULFITE AND AMMONIUM BISULFITE TO A TEMPERATURE IN THE RANGE FROM 500* TO 700* F. UNDER A SUPERATMOSPHERIC PRESSURE SUFFICIENT TO MAINTAIN TO A PART OF THE WATER IN LIQUID PHASE. 